From 16e7025255a9af2b9152adbb6780068560553613 Mon Sep 17 00:00:00 2001
From: Vlaho Poluta <vlaho.poluta@infinum.hr>
Date: Thu, 23 Nov 2023 09:44:44 +0100
Subject: [PATCH] Enabling multiple output formats to be used at the same time
 (#2872)

* Expose output format to be able to have multiple multiple formats

* Fix hound reported issue

* Fix failing test by lazy reading of Settings.audioFormat
---
 .../AudioKit/Internals/Engine/AudioEngine.swift    | 14 ++++++++++----
 Sources/AudioKit/Nodes/Mixing/MatrixMixer.swift    |  3 +++
 Sources/AudioKit/Nodes/Mixing/Mixer.swift          |  3 +++
 Sources/AudioKit/Nodes/Mixing/Mixer3D.swift        | 14 +++++++-------
 4 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/Sources/AudioKit/Internals/Engine/AudioEngine.swift b/Sources/AudioKit/Internals/Engine/AudioEngine.swift
index d0980a9ef8..78c56d17cf 100644
--- a/Sources/AudioKit/Internals/Engine/AudioEngine.swift
+++ b/Sources/AudioKit/Internals/Engine/AudioEngine.swift
@@ -69,6 +69,10 @@ public class AudioEngine {
     /// Main mixer at the end of the signal chain
     public private(set) var mainMixerNode: Mixer?
 
+    /// Output format to be used when making connections to the output
+    public var outputAudioFormat: AVAudioFormat?
+    private var outputFormat: AVAudioFormat { outputAudioFormat ?? Settings.audioFormat }
+
     /// Input node mixer
     public class InputNode: Mixer {
         var isNotConnected = true
@@ -122,7 +126,8 @@ public class AudioEngine {
 
                 // has the sample rate changed?
                 if let currentSampleRate = mainMixerNode?.avAudioNode.outputFormat(forBus: 0).sampleRate,
-                   currentSampleRate != Settings.sampleRate
+                   let currentChannelCount = mainMixerNode?.avAudioNode.outputFormat(forBus: 0).channelCount,
+                   (currentSampleRate != outputFormat.sampleRate || currentChannelCount != outputFormat.channelCount)
                 {
                     Log("Sample Rate has changed, creating new mainMixerNode at", Settings.sampleRate)
                     removeEngineMixer()
@@ -139,15 +144,16 @@ public class AudioEngine {
     }
 
     // simulate the AVAudioEngine.mainMixerNode, but create it ourselves to ensure the
-    // correct sample rate is used from Settings.audioFormat
+    // correct sample rate is used from outputFormat (default: Settings.audioFormat)
 	private func createEngineMixer() {
 		guard mainMixerNode == nil else { return }
 
 		let mixer = Mixer(name: "AudioKit Engine Mixer")
+        mixer.outputFormat = outputFormat
 		avEngine.attach(mixer.avAudioNode)
 		avEngine.connect(mixer.avAudioNode,
 						 to: avEngine.outputNode,
-						 format: Settings.audioFormat)
+						 format: outputFormat)
 
 		mainMixerNode = mixer
 	}
@@ -201,7 +207,7 @@ public class AudioEngine {
         do {
             avEngine.reset()
             try avEngine.enableManualRenderingMode(.offline,
-                                                   format: Settings.audioFormat,
+                                                   format: outputFormat,
                                                    maximumFrameCount: maximumFrameCount)
             try start()
         } catch let err {
diff --git a/Sources/AudioKit/Nodes/Mixing/MatrixMixer.swift b/Sources/AudioKit/Nodes/Mixing/MatrixMixer.swift
index 9c096f9308..3ddb0b7b80 100644
--- a/Sources/AudioKit/Nodes/Mixing/MatrixMixer.swift
+++ b/Sources/AudioKit/Nodes/Mixing/MatrixMixer.swift
@@ -33,6 +33,9 @@ public class MatrixMixer: Node {
     public var connections: [Node] { inputs }
     public var avAudioNode: AVAudioNode { unit }
 
+    /// Output format to be used when making connections from this node
+    public var outputFormat = Settings.audioFormat
+
     public let unit = instantiate(
         componentDescription:
             AudioComponentDescription(
diff --git a/Sources/AudioKit/Nodes/Mixing/Mixer.swift b/Sources/AudioKit/Nodes/Mixing/Mixer.swift
index fa97e0bfb9..8d4541af09 100644
--- a/Sources/AudioKit/Nodes/Mixing/Mixer.swift
+++ b/Sources/AudioKit/Nodes/Mixing/Mixer.swift
@@ -15,6 +15,9 @@ public class Mixer: Node, NamedNode {
     /// Underlying AVAudioNode
     public var avAudioNode: AVAudioNode
 
+    /// Output format to be used when making connections from this node
+    public var outputFormat = Settings.audioFormat
+
     /// Name of the node
     open var name = "(unset)"
 
diff --git a/Sources/AudioKit/Nodes/Mixing/Mixer3D.swift b/Sources/AudioKit/Nodes/Mixing/Mixer3D.swift
index bbc8731663..7bcf2bcc32 100644
--- a/Sources/AudioKit/Nodes/Mixing/Mixer3D.swift
+++ b/Sources/AudioKit/Nodes/Mixing/Mixer3D.swift
@@ -19,14 +19,14 @@ public class Mixer3D: Mixer {
 
 	fileprivate let mixerAU = AVAudioMixerNode()
 
-	public var outputFormat: AVAudioFormat {
-		guard let monoFormat = AVAudioFormat(
+	override init(volume: AUValue = 1.0, name: String? = nil) {
+        super.init(volume: volume, name: name)
+
+		outputFormat = AVAudioFormat(
 			standardFormatWithSampleRate: Settings.audioFormat.sampleRate,
-			channels: 1) else {
-			return Settings.audioFormat
-		}
-		return monoFormat
-	}
+			channels: 1
+		) ?? Settings.audioFormat
+    }
 
 	// MARK: - 3D Mixing Properties